Ive heard various things like vacuum tests, to apply vacuum to the egr valve at idle or drive or something like that, but how exactly do you test that? Are there any other ways to test it? My nox level during smog is always high, and everything else is really low. Also, it idles a little eratically, and after long straight drives it will act up like surge here and there, or even almost stall after i come to a stop. I have a positive backpressure egr vavle for my 1987 Lg4 camaro. Is it possible i could have the wrong egr valve? Is it possible that i could have a bad egr selenoid without tripping a trouble code? This car sometimes drives me nuts!